The development of advanced microelectronic devices is often constrained by advances in novel fabrication techniques and the development of the associated fabrication equipment. Identification of device goals such as high speed electronics, 256 Mb and greater DRAMs and equivalent logic integrated circuits requires processing of sub-half micron features and the associated sequential processing used in cluster tool systems, as described in "MESC: Is It Working?", Semiconductor International, October 1991, pp. 66-70. This trend toward single wafer processing in modular cluster tool systems rather than batch processing of wafers is due to the need to precisely control the chemical and physical microfabrication process recipe. This imposes a major constraint on the neutralization and disposal of the toxic, corrosive and flammable gases used in device fabrication. Conventional rooftop scrubbers attached to a cluster tool system can effect back pressure and gas flow between modules, ultimately prohibiting control of the separate fabrication process recipes. In addition, such gas abatement schemes may allow mixing of incompatible gases or reaction by-products. Point-of-use scrubbing of process gases is required to decouple the effects of gas abatement on the fabrication process itself, and prevent incompatible mixing of gases.
One group of gases that is commonly used in microelectronic fabrication systems are the chlorofluorocarbons. Recent studies have, however, emphasized the current concern over the use of chlorofluorocarbons (CFCs) and their effect on our environment, please refer to "Summary of the U.S. National Academy of Sciences Report: Stratospheric Ozone Depletion by Halocarbons: Chemistry and Transport", by H. I. Schiff in A. C. Aikin, editor, Proceedings of the NATO Advanced Study Institute on Atmospheric Ozone: Its Variation and Human Influences, FAA-EE-80-20, May 1980, pp. 967-975; "The Changing Atmosphere", by T. E. Graedel et al. in Scientific American, vol. 261, 1989, pp. 58-68; "The Antarctic Ozone Hole", by R. S. Stolarski, in Scientific American, vol. 258, 1988, pp. 30-36; "Nimbus 7 Satellite Measurements of the Springtime Antarctic Ozone Decrease", by R. S. Stolarski et al. in Nature, vol. 322, 1986, pp. 808-811; "Large Losses of Total Ozone in Antarctica Reveal Seasonal C1O.sub.x /NO.sub.x Interaction", by J. C. Farman et al. in Nature, vol. 315, 1985, pp. 207-210; "Charting the Ozone Alert", by R. N. Dubinsky, in Lasers and Optronics, vol. 8, 1989, pp. 45-54; "Stratospheric Sink for Chlorofluoromethanes: Chlorine AtomC-atalyzed [sic] Destruction of Ozone"by M. J. Molina et al, in Nature, vol. 249, 1974, pp. 810-812; "Global Trends in Total Ozone", by K. P. Bowman, in Science, vol. 239, 1988, pp. 48-50 ; and "Science of the Ozone Layer", by W. F. J. Evans, in Chinook, vol. 10, 1988, pp. 28-33.
In particular, the destruction of the earth's ozone layer has been attributed to the release of the chlorofluorocarbon gases into the atmosphere where they subsequently react with the ozone. Any decrease in stratospheric ozone may have serious effects since it influences weather patterns and shields the earth's surface from solar ultraviolet (UV) radiation. The latter could elevate the incidence of skin cancer and cataracts in humans, and may damage crops and phytoplankton (the basis of the oceanic food chain). In addition, rising levels of CFCs, together with methane (CH.sub.4) nitrous oxide (N.sub.2 O) and carbon dioxide (CO.sub.2) are enhancing the greenhouse effect, see above referenced article by Stolarski.
Furthermore, disruptions in weather patterns at the earth's poles, whose cold temperatures enhance the ozone depletion reactions, may have strategic implications for these regions. To date, the extent of ozone depletion has been most dramatic over Antarctica, where an ozone hole has appeared each southern spring since 1975, see the above referenced articles by T. E. Graedel et al., R. S. Stolarski, R. S. Stolarski et al., J. C. Farman et al., and "Excimer and Dye Lasers Sensing the Atmosphere", in Lambda Highlights, edited by U. Brinkmann, Gottingen, FRG, published by Lambda Physik GmbH, August 1988, pp. 1-3. In the past decade springtime ozone levels have diminished by about 50% over Antarctica. Preliminary global studies have shown depletions of from 2 to 10% have begun to occur during the winter and early spring in the middle to high latitudes of the northern hemisphere, see above referenced article by T. E. Graedel et al. For these reasons, there has been international cooperation to control the use of CFCs as exemplified by the 1987 Montreal Protocol, see above referenced article by R. N. Dubinsky. Potential regulations over the use and release of these gases may adversely affect many industries if the use and disposal of CFCs is not an environmentally sound technology.
CFCs are compounds containing chlorine (Cl), fluorine (F), carbon (C) and sometimes hydrogen (H). They are normally nontoxic, inert and cheap to manufacture. Their uses range from refrigerator coolants, cleaning solutions, propellants, plasma etchants in the microelectronics industry, and standard ingredients in plastic foams. The characteristics that make the CFCs inert allows them to remain in the free state for more than 100 years after being released into the troposphere, see above reference article by M. J. Molina et al. and "Release of Industrial Halocarbons and Tropospheric Budget", in above referenced book by A. C. Aikin, editor, pp. 373-396. The CFCs slowly percolate into the stratosphere where the ozone layer resides from 15 to 50 kilometers above the earth's surface. Here, absorption of solar UV photons and subsequent dissociation results in destruction of the ozone catalytically by substances such as Cl and C10.sub.x. Stratospheric ozone (O.sub.3) is formed when an oxygen molecule (O.sub.2) is dissociated by solar UV radiation, the free oxygen atoms can then combine with another oxygen molecule to form ozone: EQU O.sub.2 +h.nu..fwdarw.0+0 (1) EQU 0+0.sub.2 .fwdarw.0.sub.3. (2)
Usually, photochemical reactions catalyzed by nitrous oxides (NO.sub.x) remove ozone at a rate equal to the rate of its formation. Chlorine catalytic cycles can disturb this natural balance. The role of CFCs is that of a source of atomic chlorine which begins a cycle of chemical reactions, destroying ozone. An example of a common CFC released into the troposphere is dichlorodifluoromethane (CF.sub.2 Cl.sub.2). Stratospheric photolytic dissociation by solar radiation creates two odd-electron species, one chlorine atom and one free radical: EQU CF.sub.2 Cl.sub.2 +h.nu..fwdarw.CF.sub.2 Cl. (3)
The cycle begins with the breakup of ozone by atomic chlorine and the formation of chlorine monoxide (ClO) and molecular oxygen (O.sub.2): EQU Cl+O.sub.3 .fwdarw.ClO+O.sub.2. (4)
Then the chlorine monoxide reacts with an oxygen atom formed by the photodissociation of another oxygen molecule (reaction equation [1] above) and liberates the chlorine which can initiate the cycle again: EQU ClO+O.fwdarw.Cl+O.sub.2. (5)
Under most conditions of the earth's ozone layer, reaction equation (5) above is a slower reaction than (4) because there is much lower concentration of oxygen atoms (O) than ozone (O.sub.3).
Chlorine monoxide reactions with nitrogen oxides are a competing reaction that can remove chlorine from this cycle by combining to form chlorine nitrate (ClNO.sub.3), see above referenced article by M. J. Molina et al. and "Free Radicals in the Earth's Stratosphere: A Review of Recent Results", by J. G. Anderson, in above referenced book edited by A. C. Aikin, pp. 233-251. However, at stratospheric temperatures ClO reacts with O six times faster than NO.sub.2 reacts with O. Consequently, the Cl-ClO chain can be considerably more efficient than the NO-NO.sub.2 chain in catalytic conversion of O.sub.3 +O.fwdarw.2O.sub.2 per unit time, see above referenced article by M. J. Molina et al. It is generally agreed that after studies of the relative reaction rates described above, ClO.sub.x and Cl molecules from CFCs are the cause of stratospheric ozone depletion.
Users of large volumes of chlorofluorocarbons must currently release CFCs into the atmosphere because they cannot be decomposed and removed from the "waste" gases used in their particular process. Conventional scrubbers, filters, and CDOs (Controlled Decomposition and Oxidation Chambers or "burn boxes") are used to remove most toxic, corrosive and flammable gases used in industrial applications but do not affect chlorofluorocarbons because they are inert.
Recent advances in dry etching of silicon and silicon-on-sapphire also use gases such as nitrogen trifluoide and other halocarbons which cannot be hydrolyzed (scrubbed) by conventional techniques, and therefore pose a threat to personnel and the environment if not abated, see "Toxic Gas: A Cause for Alarm" Semiconductor International, November 1991, pp. 68-72. Since cluster tool fabrication systems employ both deposition and etching reactions required for microelectronic device fabrication, abatement schemes compatible with processing other gases such as silane, germane, and dichlorosilane which are normally decomposed using CDOs are desirable.
Thus, a continuing need exists in the state of the art for a gas abatement system which is amenable to point-of-use decomposition to avoid the above cluster tool system problems and which can treat nonhydrolyzable ambients as required for advanced silicon and silicon-on-sapphire microelectronic device processing. A photon controlled technique herein is described to induce decomposition of nonhydrolyzable ambients whereby the gaseous or liquid--are broken down and the by-products are subsequently hydrolyzed and disposed of by conventional means, and is amenable for point-of-use process gas abatement.